Design of Transformer Shielding Foil Structure for Minimizing Common-Mode Noise in LLC Resonant Converters

The common-mode (CM) noise in LLC resonant converters is mainly caused by the high-frequency voltage change of power semiconductor devices in the primary and secondary circuits. Using transformer shielding foil is an important method to suppress the CM noise in LLC resonant converter. For mitigating CM noise effectively, the shielding foil structure of LLC transformer should be carefully designed. In this paper, the equipotential distribution and structural capacitance of LLC transformer windings were analyzed. Based on this, a method was proposed to calculate the optimal structure of shielding foil. This is realized through analyzing the relation between the width of shielding foil and CM current. The proposed method is validated by comparison of calculated and measured results.